At present, a wireless communication system, such as a cellular phone system or a wireless local area network (LAN), has been widely used. Also, in the field of the wireless communication, in order to further improve a communication speed or a communication capacity, discussions for the next generation communication are continuously being made. For example, standardization of a communication standard called long term evolution (LTE) or a communication standard based on the LTE, which is called LTE-Advanced (LTE-A), has been completed or is being studied by 3rd Generation Partnership Project (3GPP) which is a standardization organization.
In such a wireless communication system, a communication terminal may perform a cell search process at the time of power-up or stand-by, or during a communication. In the cell search process, processing such as detection of a frame timing or a cell ID (identification) is carried out according to, for example, a synchronizing signal included in a radio signal. The communication terminal may send or receive a radio signal through the cell search in synchronization with a base station, and may also acquire basic information in a case of a wireless communication.
In the cell search processing, for example, there are three types of processing, such as carrier search (hereinafter, may be referred to as a band search) processing, initial cell search processing, and peripheral cell search processing.
The band search process is, for example, processing for specifying a carrier frequency used for a wireless communication by a mobile terminal before the initial cell search process is performed. The initial cell search process is, for example, processing for acquiring a frame timing, a symbol timing, a use frequency, a cell ID (identification) according to the carrier frequency specified in the band search process. For example, the communication terminal may efficiently detect the carrier frequency at the initial cell search process by performing the initial cell search process after the band search process.
The peripheral cell search process is performed when the communication terminal performs a wireless communication with the base station. By the peripheral cell search process, for example, the communication terminal may acquire a maximum of 5 IDs of other cells.
The communication terminal performs a cell search by using a synchronizing signal included in the radio signal. In a 3G system, such as a wideband code division multiple access (W-CDMA), or in an LTE system, two types of synchronizing signals are used.
FIGS. 26A and 26B, and FIGS. 27A and 27B illustrate exemplary configurations of a radio frame in a 3G system and an LTE system, respectively.
As illustrated in FIGS. 26A and 26B, in the 3G system, 15 slots are included within one radio frame. A primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH) are included in a head symbol of each slot. The communication terminal detects a first synchronizing signal by using a P-SCH (or may be referred to as a primary synchronization channel (PSC)). Also, the communication terminal detects a second synchronizing signal by using a S-SCH (or may be referred to as a secondary synchronization channel (SSC)). The communication terminal performs a cell search by using the first synchronizing signal and the second synchronizing signal.
As illustrated in FIGS. 27A and 27B, in the LTE system, one radio frame includes 10 sub-frames, each sub-frame includes two slots, and each slot includes seven symbols. The 6th and 7th symbols of a first slot as a head include an S-SCH and a P-SCH, respectively. Also, the 6th and 7th symbols of an 11th slot from the head include an S-SCH and a P-SCH, respectively. The communication terminal detects a primary synchronization signal (PSS: hereinafter, may be referred to as a first synchronizing signal) by using the P-SCH. The communication terminal also detects a secondary synchronization signal (SSS: hereinafter, may be referred to as a second synchronizing signal) by using the S-SCH. The communication terminal performs a cell search by using the first synchronizing signal and the second synchronizing signal.
In any system, in the initial cell search process, the communication terminal detects, for example, a symbol timing by using a first synchronizing signal in a first step. Then, the communication terminal detects, for example, a frame timing or a cell ID group by using a second synchronizing signal in a second step, and specifies a scrambling code.
As for a technology on such a wireless communication, for example, there are the following technologies.
That is, there is a mobile wireless terminal in which correlation values with all synchronization codes for each slot are detected, deviations thereof are calculated, and frame correlation values corresponding to scrambling code group numbers are detected, so that a frame timing is detected by the corresponding correlation value.
According to this technology, it is possible to provide a mobile terminal device capable of detecting a frame timing with a high precision regardless of changes in a radio propagation environment.
Also, there is a receiving device of a CDMA cellular system in which after a correlation with a reference numeral in response to a baseband signal is made, an output signal is output to a plurality of notice channel demodulating units or a plurality of speech channel demodulating units under the control by a controller, so as to be processed in each of the demodulating units.
According to this technology, it is possible to shorten a time required for the cell search without increasing the size of the circuit.
Furthermore, there is a technology on a mobile station device configured to perform a cell search after performing a carrier search, in which when the carrier search is performed, received power measurement is carried out in an allocated frequency bandwidth, and a range for searching the service carrier is limited to the vicinity of a frequency where the received power exceeds a threshold.
According to this technology, it is possible to provide a mobile station device capable of efficiently performing a carrier search, shortening a time for detecting a service carrier, and reducing power consumption by reducing the number of useless cell searches, thereby prolonging a continuous stand-by time.
Related technologies are disclosed in Japanese Laid-Open Patent Publication No. 2002-185441, Japanese Laid-Open Patent Publication No. 11-191896, Japanese Laid-Open Patent Publication No. 2003-60551